Recently, as a result of the development of high transmitting speed optical communications systems which ease network structure being developed, optical communication techniques are required to construct the optic fiber, the light source and the optical detector as well as a number of the function of an optical components. The optical switch and a wavelength divider etc. is to change the transmission path passing through the light in the optical divider and the optical coupler for dividing and coupling the optical signal with the optical components.
The optical switch of a number of the optical components is very important in order to freely switch to another transmission line according to the requirement thereof if any transmission line fails.
The optical switch is generally separated into the bulk type of the optical switch position and the waveguide path type of the optical switch position.
The bulk type of the optical switch has the advantage of having a small wavelength dependence and a relative low loss features by using a moving prism and lens, but it is not amenable to a production on a large scale because the assembly and the adjusting process thereof are complex and expensive.
However, the waveguide path type of the optical switch is amenable to by producing on a large scale easily since it is fabricated by using the fabrication technique of the semiconductor device.
The waveguide path type of the conventional optical switch is discussed in an article entitled "Silica waveguide on silicon and their application to integrated optic components", Optical and Quantum Electronics, Volume 22 (1990), pages 391-416.
The optical switch is sequentially deposited on a lower clad layer and the silica layer of the silicon oxide layer on the silicon substrate by the flame hydrolysis deposition method, and the silica layer is patterned by the Reactive Ion Etching(RIE) method, and forms the channel waveguide path.
An upper clad layer covering the channel waveguide path is deposited on the lower clad layer, in which the upper clad layer is formed to the thickness of 30 .mu.m or more so that the surface thereof can be planed.
Then, a heater switching mechanism to change the phase of the optical signal transmitted by adjusting the temperature of the channel waveguide path is formed on the channel waveguide path and the corresponding upper clad layer.
However, the waveguide path type of the optical switch as mentioned hereinabove has a problem in which the heat diffuses when any of the channel waveguide paths apply the heat. The diffused heat changes the phase of the optical signal transmitted by heating those together with the neighboring channel waveguide path because the upper clad layer has been formed too thickly, thereby generating the crosstalk.
The heat generated by the thick upper clad layer at the thin film heater is the problem because it slows too much the switch velocity since the velocity to be delivered to the channel waveguide path slows. Also the operational power is large to deliver to the channel waveguide path under the condition in which the heater generating at the thin film heater must be high.